#include <bits/stdc++.h>
using namespace std;
double s(double a,double b,double c)
{
	double s=0,p=0;
	p=(a+b+c)/2;
	s=sqrt(p*(p-a)*(p-b)*(p-c));
	return s;
}
int main()
{
    double b1,b2,b3,b4,b5,b6,b7;
	cin>>b1>>b2>>b3>>b4>>b5>>b6>>b7;
    double s1=0,s2=0,s3=0,ans=0;
    s1=s(b1,b5,b6);
    s2=s(b2,b7,b6);
    s3=s(b3,b4,b7);
    ans=s1+s2+s3;
    cout<<fixed<<setprecision(3)<<"s="<<ans<<endl;
    return 0;
}